Question

speed of boat in still water is 5km/h. it crosses river of width 1km along shortest path in 15 min find velocity of river

Answer 1

speed of boat at still water = 5 km/h

width of the river = 1 km

time of crossing the river = 15 minutes

solve for the velocity of the water = Vw

Solving for the resultant velocity Rv :

Rv = distance traveled / time of travel

Rv = 1 km / 15 minutes

Rv = 1 km / 0.25 h

Rv = 4 km/h

Solving for the velocity of water , Vw

Rv^2 = Vboat^2 - Vw^2

4^2 = 5^2 – Vw^2

16 = 25 – Vw^2

Vw^2 = 25-16

Vw^2 = 9

Vw = 3 km/h is the velocity of the river water

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Answer 2

Answer:

The velocity of river stream is 3 km/hr.

Explanation:

The speed of the boat along the shortest possible path

$AB = \frac{1}{\frac{15}{16} } = 4 km/hr$

Now, The velocity of river water

$V = \sqrt{5^{2}-4^{2} } = \sqrt{25-16} = \sqrt{9} = 3 km/hr$